Janus and Henderson just surprised the market with a $6 billion transatlantic merger

LONDON — The US asset manager Janus Capital and its London-listed rival Henderson Global Investors on Monday said they had agreed to an all-share $6 billion merger, sending Henderson's shares soaring.

The merger will enable the group to cut costs and increase diversification, Henderson CEO Andrew Formica told a media call, and comes as the industry looks to streamline operations to protect margins amid widespread pressure on fees.

"The combined product lineup will be much more balanced and diverse," he said. The combined company would manage more than $320 billion in assets, the firms said.

Formica told CNBC that bond king Bill Gross, who works at Janus, is "very, very supportive" of the deal. "He sees it as just improving already on the strength of Janus, of what he's already seen since he's been there and he can see with the combination with Henderson can just make it an even stronger and better business."

Henderson and Janus shareholders are expected to own approximately 57% and 43%, respectively, of Janus Henderson Global Investors' shares, with the merger completing in the second quarter of 2017, subject to regulatory approvals.

The combined group will apply for a primary listing in New York, keeping Henderson's Australian listing but delisting in London. Henderson is in the FTSE 250 market segment.

The merger will involve a share exchange in which each Janus share will be exchanged for 4.719 newly issued shares in Henderson, the firms said in a statement.

"We see this as a positive move with complementary asset bases and a very material cost synergy figure," analyst Paul McGinnis at Shore Capital said in a client note.

The firms said they were targeting an annual run rate in net cost synergies of at least $110 million, representing about 16% of the combined group's underlying earnings before interest, taxes, depreciation, and amortization.